Short-chain Perfluorocarboxylic Acids Research Articles

Theoretical and experimental insights into the mechanisms of C6/C6 PFPiA degradation by dielectric barrier discharge plasma

As an emerging alternative legacy perfluoroalkyl substance, C6/C6 PFPiA (perfluoroalkyl phosphinic acids) has been detected in aquatic environments and causes potential risks to human health. The degradation mechanisms of C6/C6 PFPiA in a dielectric barrier discharge (DBD) plasma system were explored using validated experimental data and density functional theory (DFT) calculations. Approximately 94.5% of C6/C6 PFPiA was degraded by plasma treatment within 15 min at 18 kV. A relatively higher discharge voltage and alkaline conditions favored its degradation. C6/C6 PFPiA degradation was attributed to attacks of •OH, •O2−, and 1O2. Besides PFHxPA and C2 −C6 shorter-chain perfluorocarboxylic acids, several other major intermediates including C4/C6 PFPiA, C4/C4 PFPiA, and C3/C3 PFPiA were identified. According to DFT calculations, the potential energy surface was proposed for possible reactions during C6/C6 PFPiA degradation in the discharge plasma system. Integrating the identified intermediates and DFT results, C6/C6 PFPiA degradation was deduced to occur by stepwise losing CF2, free radical polymerization, and C-C bond cleavage. Furthermore, the DBD plasma treatment process decreased the toxicity of C6/C6 PFPiA to some extent. This study provides a comprehensive understanding of C6/C6 PFPiA degradation by plasma advanced oxidation.

Theoretical and experimental insights into electron-induced efficient defluorination of perfluorooctanoic acid and perfluorooctane sulfonate by mesoporous plasma

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are global environmental pollutants and pose significant threats to environmental safety and human health. Defluorination of PFOA and PFOS was investigated theoretically and practically in a mesoporous plasma system in this study. Rapid and highly efficient defluorination was realized, and 98% and 65% defluorination rate for PFOA and PFOS, respectively, were obtained within 60 min of treatment. Electrons generated in the mesoporous plasma system played a decisive role in PFOA and PFOS defluorination; other species, including 1O2 and ·OH, also contributed to defluorination. C-F, C-C, and C-S bonds were broken by plasma oxidation; various shorter-chain perfluorocarboxylic acids, polyfluoroalkyl substances, and alcohols were produced. PFOA and PFOS decomposition mechanisms involved electron transfer, defluorination, decarboxylation, and hydroxylation reactions. Desulfonation reactions were also involved in PFOS decomposition. Density functional theory calculations identified sites susceptible to be attacked and the main degradation pathways. Effective defluorination of PFOA and PFOS reduced their toxicities. Furthermore, its potential for actual surface water treatment was also determined.

PFAS treatment with granular activated carbon and ion exchange resin: Comparing chain length, empty bed contact time, and cost

Per- and polyfluoroalkyl substances (PFASs) are among the most recalcitrant chemicals ever manufactured and are associated with substantial global environmental challenges. PFAS removal performance of granular activated carbon (GAC) and ion exchange resin (IX) was evaluated and compared using a segmented column system with full scale media under continuous flow conditions. Results from the PFAS breakthrough analysis established via column operation under different empty bed contact times (EBCTs) was used to characterize the mass transfer zone (MTZ) of multiple PFASs and evaluate optimum EBCTs for GAC and IX treatment. The height of the MTZ corresponded to PFAS chain length and functional group, where the poorly removed short chain perfluoro-carboxylic acids exhibited the longest MTZ. Elongated PFAS MTZs justified longer EBCTs required for treatment of short chain PFAAs compared to long chain PFAAs for GAC and IX. In addition, a cost sensitivity analysis was employed to demonstrate how unit media cost, changeout frequency, and treatment goal feasibility dictated annual operation and maintenance (O&M) costs associated with GAC and IX installations. IX was found to the most cost-effective adsorbent for the removal of long and short chain PFASs compared to GAC. Results from the cost analysis indicated that adsorbent selection was the most critical factor dictating treatment cost with marginal impact from unit media cost or expected changeout frequency.

Temporal trends of perfluoroalkyl substances in an Australian wastewater treatment plant: A ten-year retrospective investigation

Per- and poly-fluoroalkyl substances (PFAS) are a problematic group of chemicals used in various industrial and household products. They have been extensively detected in wastewater as a result of day-to-day product usage. Due to concerns about their safety, voluntary and regulatory action to limit the manufacture and use of some individual PFAS has occurred since the year 2000. The impact that this intervention has had on the use and potential exposure of Australians has not been measured. Wastewater serves as a powerful tool to assess the chemical use or consumption patterns of a population over time. We accessed a ten-year wastewater archiving program to conduct a temporal analysis of PFAS trends in an urban Australian population between the years 2010 and 2020. Results showed a decline in the concentrations for most PFAS, and a change in the PFAS profile from perfluorosulfonic acids and long-chain perfluorocarboxylic acids, to the short-chain perfluorocarboxylic acids and PFOS-replacement degradation products such as 5:3 FTCA. Intermittent pulses of PFAS that were significantly higher than ‘background’ levels (i.e., representing the PFAS input from primarily households) were observed, suggesting continuing industrial PFAS input within the wastewater catchment. This study highlights the long-term consequences of the diffuse use of persistent chemicals in products, and their ability to continue to enter the wastewater stream for decades.

Insights into the degradation mechanism of perfluorooctanoic acid under visible-light irradiation through fabricating flower-shaped Bi5O7I/ZnO n-n heterojunction microspheres

• Bi 5 O 7 I/ZnO n-n heterojunction was facilely prepared by in-situ phase transition. • n-n Bi 5 O 7 I/ZnO efficiently degraded PFOA under visible light irradiation. • The experimental mechanism was verified by DFT calculation. • h + were the active substance responsible for PFOA degradation. Perfluorooctanoic acid (PFOA), which is an emerging contaminant, has received extensive attention in recent times due to its high toxicity and environmental risk. In this study, BiOI supported on Zn-Al hydrotalcite (BOI 0.04 -BHZA) was calcined at 400 ℃ to obtain flower-shaped Bi 5 O 7 I/ZnO n-n heterojunction microspheres for the photocatalytic degradation of PFOA under visible light irradiation. The samples were characterized by X-ray diffraction, Fourier transform infrared, UV–vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Compared with BOI (k 1 = 0.0044 h −1 ), BHZA (k 2 = 0.0054 h −1 ), and BOI 0.04 -BHZA (k 3 = 0.0073 h −1 ), the degradation rate constant of Bi 5 O 7 I/ZnO n-n heterojunction microspheres (k 4 = 0.013 h −1 ) increased by 2.9, 2.4, and 1.8 times, respectively. Approximately 91% of PFOA was degraded after 6 h of irradiation. The excellent photocatalytic performance was ascribed to the Bi 5 O 7 I/ZnO n-n heterojunction formed by calcination, which enlarged the photoresponse to the visible light region and increased the separation efficiency of electron-hole pairs. Moreover, the degradation pathway of PFOA was investigated using high-performance liquid chromatography-mass spectrometry and ion chromatography assisted by density functional theory calculations. The results demonstrated that the carboxylic groups of PFOA was vulnerable to attack by the photoproduction hole. The formed unstable perfluoroheptyl radicals transformed into shorter chain perfluorocarboxylic acids by the elimination of CF 2 units. It was expected that this Bi 5 O 7 I/ZnO n-n heterojunction photocatalyst would be a promising candidate for PFOA treatment.

Occurrence of per- and polyfluoroalkyl substances and unidentified organofluorine in leachate from waste-to-energy stockpile - A case study

Per- and polyfluoroalkyl substances (PFASs) are a diverse group of chemicals used in consumer products, which will inevitably end up in waste streams. Landfills are widely recognized secondary point sources of PFASs, but other types of waste management sites have received less attention. Therefore, in a case study presented here we investigated releases of PFASs from temporarily stored waste by determining quantities of 34 PFASs in leachate from a Waste-to-Energy stockpile (45 000 ± 2000 tonnes) during five months in 2019. We also measured extractable organofluorine (EOF) to account for PFASs not included in the target list. The mean total concentration of the 34 PFAS (Σ34PFAS) was 211 ± 31 ng/L, and short-chain (C4–C7) perfluorocarboxylic acids (PFCAs) accounted for 56–60% of the total. Moreover, we found that Σ34PFAS only accounted for 12% ± 4% of EOF detected in the leachate. Our results demonstrate that waste stockpiles are previously unexplored sources of PFASs in the environment, and the dominance of short-chain PFCAs is consistent with observed profiles of contaminants in landfill leachates.

Perfluoroalkyl acid (PFAA) profile and concentrations in two co-occurring tit species: distinct differences indicate non-generalizable results across passerines

Eggs of terrestrial bird species have often been used to biomonitor both legacy and emerging anthropogenic contaminants, such as perfluoroalkyl acids (PFAAs). However, few, if any, studies have examined whether results obtained in a given model species can be generalized across bird species. Therefore, we compared potential differences in egg PFAA profile and concentrations between two widely studied passerine species, great tit (Parus major) and blue tit (Cyanistes caeruleus), which are similar in many aspects of their ecology and life history. Whole clutches of both species were collected from the same breeding season and at the same place (Antwerp, Belgium), enabling us to study laying order effects. Additionally, we evaluated how egg PFAA concentrations for both species changed along a distance gradient from a PFAA point source. Although the sum PFAA concentrations did not significantly differ between great tits and blue tits, large differences in PFAA profile and laying order effects were observed. Great tits showed a more diverse PFAA detection profile, including perfluorooctane sulfonic acid (PFOS) and various long-chain perfluorocarboxylic acids (PFCAs) but no short-chain compounds. Contrarily, short-chain PFCAs (perfluorobutanoic acid (PFBA) and perfluorohexanoic acid (PFHxA)) were only detected in blue tit eggs. The variation of perfluorooctanoic acid (PFOA) concentrations within clutches was large in both species, although laying order effects on PFOA concentrations were only found in blue tits. Although egg PFOA concentrations of both species decreased similarly from the fluorochemical point source onwards, more variation in egg PFOA concentrations could be explained by distance from the fluorochemical plant in great tits (60%) than in blue tits (15%). Results showed that both species markedly differed in terms of egg PFAA profile and concentrations, most likely reflecting differences in diet, foraging habits and egg protein composition. Finally, biomonitoring results of PFAAs in eggs are likely not generalizable across bird species.

Hydrated-electron-based short chain perfluorosulfonic acid decomposition in VUV/sulfite system

Abstract Perfluorosulfonic acids (PFSAs) have attracted increasing attention due to their global distribution, high chemical stability and persistence. As a powerful reductant, hydrated electron () shows extraordinary reactivity towards halogenated organic substances like PFSAs. In this study, -based photo-decomposition of perfluorohexane sulfonate (PFHxS) in a VUV/sulfite system was investigated. The kobs of PFHxS decomposition in the studied system was 0.0049 ± 0.0005 min−1, which was 24.5-fold faster than that in a sole VUV system. It was demonstrated that was the main reactive species responsible for PFHxS decomposition. PFHxS decomposition kinetics were accelerated at higher initial solution pH and sulfite dosage, but were restrained when higher initial PFHxS concentration was introduced. Co-existence of chloride showed slight enhancement of PFHxS decomposition, whereas nitrate and bicarbonate suppressed PFHxS decomposition. Accompanying PFHxS decomposition, short chain perfluorocarboxylic acids (PFCAs) were detected as main intermediate products. PFHxS decomposition started with C-S bond fracture, followed by perfluoroalkyl radical hydrolysis reactions and perfluorohexanoic acid (PFHxA) formation. Afterwards, PFHxA was defluorinated by stepwise loss of CF2 units to generate other short chain PFCAs.

Effect of substrate concentrations on aerobic biotransformation of 6:2 fluorotelomer sulfonate (6:2 FTS) in landfill leachate

Biotransformation of 6:2 fluorotelomer sulfonate (FTS) results in the formation of short-chain (C4 – C6) perfluorocarboxylic acids (PFCAs) in landfill leachate. Although leachate substrate concentrations (i.e., organic carbon, ammonia) vary widely, their effects on 6:2 FTS biotransformation and PFCAs formation are unknown. This study investigated the effect of organic carbon and ammonia concentration in 6:2 FTS aerobic biotransformation and PFCA formation in leachate. Biotransformation experiments were conducted with sediment collected from a landfill leachate ditch, to which deionized (DI) water and various amounts of leachate were added. Microbial community analysis using 16S rRNA indicated that while phylum Proteobacteria dominated the bacterial composition throughout the 60 days, Actinobacteria increased with time. Many genera from Proteobacteria and Actinobacteria can synthesize a wide array of enzymes, indicating that these phyla are likely to play an important role in 6:2 FTS biotransformation. Higher biotransformation of 6:2 FTS was observed in leachate-added microcosms (∼21%), compared to DI water microcosm (∼14%), likely reflecting the substrate dependency of 6:2 FTS biotransformation. Substrate limiting conditions in DI water microcosm resulted in slightly greater formation of ∑(C4 – C6) PFCAs (∼14 mol%), compared with leachate added microcosms (10–13 mol%). The findings suggest that dilution of landfill leachate, (e.g., during wet seasons), likely results in reduced 6:2 FTS biotransformation and increased PFCAs formation compared to dry conditions. Observed formation of C7 – C8 PFCAs in the live microcosms suggested that landfills act as secondary sources of legacy PFCAs (e.g., perfluorooctanoic acid) in the environment.

Analysis of 58 poly-/perfluoroalkyl substances and their occurrence in surface water in a high-technology industrial park

Poly/perfluoroalkyl substances (PFASs) have some water solubility so that they are more liable to enter surface water. A comprehensive analysis method was established to analyze 17 classes of 58 PFASs in surface water by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) after automated solid phase extraction (SPE). The method showed acceptable recoveries and precision with recoveries of 60%–130% and RSD less than 30% with a few exceptions, and method detection limits (MDLs) of 0.004 ng/L-2.0 ng/L. It was investigated the surface water around Zhangjiang High-Technology Park in Shanghai. The concentration of ∑PFASs ranged from 115 ng/L to 600 ng/L. The main pollutant was perfluoro-3-methylheptanoic acid (P3MHpA), which is isopropyl isomer of perfluorooctanoic acid (PFOA), accounting 41.6% of ∑PFASs. It was detected in all samples and its level was far higher than that of PFOA with the maximum of 432 ng/L determined surrounding integrated circuits company. Short-chain perfluorocarboxylic acids (PFCAs) and PFOA were also major constituents accounting for 39.9% of ∑PFASs. Perfluorosulfonic acid (PFSAs (C4, 6, 8)) were detected in all samples, while most concentrations were below 10 ng/L. In addition, 1H,1H,2H,2H-perfluorooctane sulfonate (6:2) (6:2 FTS), 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-propanoic acid (HFPO-DA) and 9-chlorohexadecafluoro-3-oxanonane-sulfonate (9Cl-PF3ONS) were also detected in all samples at low level. Long chain PFCAs and PFSAs and other classes of PFASs were also detected with low levels and/or low frequencies. The level of PFASs shows an increasing trend in surface water in Shanghai. The whole risk is low for residents from water exposure, while it should cautious to the emission of P3MHpA from integrated circuits and its potential risk.

Concentrations of Typical Perfluoroalkyl Acids and Contributions of Their Precursors in the Water of the Le'an River in China

Transformation of perfluoroalkyl substance (PFASs) precursors and their contribution to PFASs pollution have become a subject of great research interest. The concentration of PFASs and their precursors and the transformation of precursors in the water samples collected from Le'an River and the effluents of sewage treatment plants (STPs) were investigated based on methods including hydroxyl radical (·OH) oxidation, extraction by solid phase, and ultra-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The results of the study revealed that the PFAS concentrations were in the range of 14.89-40.84 ng·L-1and 58.63-114.87 ng·L-1, and averaged 28.76 ng·L-1 and 86.75 ng·L-1 in the water of the Le'an River and the STP effluents, respectively. The compound with the highest concentration for the two kinds of waterbodies was perfluorooctanesulfonic acid (PFOS). The PFAS concentrations showed obvious spatial differences in the water of the Le'an River. After the oxidation treatment, the PFAS concentrations clearly increased in the two kinds of waterbodies. The increased concentrations of short-chain perfluorocarboxylic acids with carbon atom numbers of 4-8 (ΣΔ［PFCAC4-C8］oxidation conversion) were higher than those of compounds with long carbon chains. However, the increased concentrations of PFCAs for the STP effluents were higher than those for the river water. The transformation ratio obtained from the increased concentration of PFCAs led by the oxidation treatment against the PFCA concentration before oxidation (ΔPFCAoxidation conversion/PFCAbefore oxidation) was lower for the STP effluents than those for the water of Le'an River, which might be induced by the precursors' degradation during the sewage treatment process.

Degradation of perfluorooctanoic acid by zero-valent iron nanoparticles under ultraviolet light

Perfluorooctanoic acid (PFOA) is ubiquitous in the environment because of its wide applications in aqueous film forming foam, food packing, waterproof breathable fabrics, and Teflon products. Though it is resistant to biodegradation, photocatalytic degradation has been proven possible. In this study, zero-valent iron nanoparticles (Fe0 NPs), with or without 1% polyvinylpyrrolidone (PVP) coating, were used for PFOA degradation under ultraviolet C (UVC) light for the first time. PFOA was degraded faster initially (e.g., < 13 h) with Fe0 NPs than without Fe0 NPs under UVC light. In addition, the degradation rate using Fe0 NPs without coating was higher than that with 1% PVP coating in the initial 6 h, although the difference was diminished afterwards. Both Fe2+ and Fe3+ ions were detected during the process. Shorter-chain perfluorocarboxylic acids (PFCAs), i.e., PFHpA, PFHxA, PFPeA, and PFBA, were detected as main intermediates; fluoride ions (F−) were also detected. Rapid consumption of Fe3+ (plus the lower UV–vis absorption intensity observed for a mixture of PFOA and FeCl3 compared to the intensity observed for FeCl3 alone) indicated the possible formation of [C7F15COO-Fe]2+—a degradable complex. The UV/Fe0 system is superior, with low toxicity of iron and no introduction of other chemicals. Additionally, the cost of Fe0 NPs is low, and the recycle of Fe0 NPs is easy from the treated water by their magnetic properties. The study provided an innovative, environment-friendly, and low-cost method for PFOA degradation by Fe0 NPs under UVC light, which could be potentially applied for treatment of surface water and groundwater contaminated by PFOA.

Destruction of Per- and Polyfluoroalkyl Substances (PFAS) with Advanced Reduction Processes (ARPs): A Critical Review.

Advanced reduction processes (ARPs) have emerged as a promising method for destruction of persistent per- and polyfluoroalkyl substances (PFAS) in water due to the generation of short-lived and highly reductive hydrated electrons (eaq-). This study provides a critical review on the mechanisms and performance of reductive destruction of PFAS with eaq-. Unique properties of eaq- and its generation in different ARP systems, particularly UV/sulfite and UV/iodide, are overviewed. Different degradation mechanisms of PFAS chemicals, such as perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), and others (e.g., short chain perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs), per- and polyfluoro dicarboxylic acids, and fluorotelomer carboxylic acids), are reviewed, discussed, and compared. The degradation pathways of these PFAS chemicals rely heavily upon their head groups. For specific PFAS types, fluoroalkyl chain lengths may also affect their reductive degradation patterns. Degradation and defluorination efficiencies of PFAS are considerably influenced by solution chemistry parameters and operating factors, such as pH, dose of chemical solute (i.e., sulfite or iodide) for eaq- photoproduction, dissolved oxygen, humic acid, nitrate, and temperature. Furthermore, implications of the state-of-the-art knowledge on practical PFAS control actions in water industries are discussed and the priority research needs are identified.

Phototransformation of perfluorooctane sulfonamide on natural clay minerals: A likely source of short chain perfluorocarboxylic acids

In this study, a new phototransformation pathway for perfluorooctane sulfonamide (FOSA) and underlying degradation mechanisms are described. Phototransformation of FOSA in a natural clay mineral (montmorillonite) suspension was compared to that in an aqueous solution. Results showed that the presence of montmorillonite can significantly promote the transformation of FOSA to perfluocarboxylic acids (increasing rate). The phototransformation reaction was found to be initiated by the activation of adsorbed oxygen molecules on the surface of montmorillonite, which generate superoxide anion and hydroxyl radicals. Hydroxyl radicals can then attack FOSA adsorbed onto the surface of montmorillonite, promoting the transformation process. In this reaction, clay minerals played a dual role: providing hydroxyl radicals and concentrating FOSA on their surfaces. This helped to promote the contact and reaction between FOSA and hydroxyl radicals. This study provides the first evidence that heterogeneous oxidation of FOSA at the surface of natural clay minerals may act as an important source of perfluocarboxylic acids (PFCAs), especially short chain PFCAs (i.e. trifluoroacetic acid, TFA).

Enhanced perfluorooctanoic acid degradation by electrochemical activation of peroxymonosulfate in aqueous solution

Perfluorooctanoic acid (PFOA) was efficiently decomposed at Ti/SnO2-Sb anode via peroxymonosulfate (PMS) activation. PFOA degradation followed both pseudo-zero-order (0–30 min) and pseudo-first-order (30–120 min) kinetics. The pseudo-first-order kinetics constant could increase to 0.0484 min−1 (3.84 times higher than that without PMS) during 30–120 min electrolysis. The inhibited performance in radical scavengers implied both sulfate radical (SO4•−) and hydroxyl radical (•OH) contributed to PFOA degradation. The •OH quantitative detection experiments demonstrated that SO4•− formed from PMS activation could promote •OH generation (from 0.12 mM to 0.24 mM). Electron spin resonance (ESR) tests further proved that SO4•− and •OH were generated during PFOA degradation. According to linear sweep voltammetry (LSV) analyses, the oxygen evolution potential (OEP) value of Ti/SnO2-Sb electrode increased from 1.59 V to 1.72 V (vs SCE) via PMS addition, indicating the inhibited oxygen evolution which was beneficial for the reactive species formation (i.e. •OH, SO4•−). On the basis of intermediates verification and mass balance of carbon and fluorine, PFOA was proposed to be oxidized into short-chain perfluorocarboxylic acids mainly by •OH and SO4•−.

Highly efficient photocatalytic degradation toward perfluorooctanoic acid by bromine doped BiOI with high exposure of (001) facet

Perfluorooctanoic acid (PFOA) is a highly persistent organic pollutant and being regulated in many countries. The strong chemical stability makes it a big challenge to degrade PFOA in aquatic environment. In this study, a high (001) facet exposed BiOI1-xBrx solid solution was successfully synthesized by doping bromine using solvothermal method. The prepared catalyst doped 5 % molar mass of Br (BiOI0.95Br0.05) displayed extremely high photocatalytic activity to PFOA under UV irradiation: 96 % of PFOA was decomposed within 120 min and ∼ 65 % was mineralized within 180 min. The reaction kinetic constant was 4.3 times that of BiOI. The enlarged specific surface area, enhanced UV-light absorption and promoted separation of electron-hole pairs were responsible for the enhanced photocatalytic activity. The photogenerated electrons and holes were the decisive species for PFOA decomposition. Short chain perfluorocarboxylic acids (PFCAs), HCOOH, and F− were generated and the possible degradation pathway of PFOA by BiOI0.95Br0.05 was proposed.

Highly efficient degradation of perfluorooctanoic acid: An integrated photo-electrocatalytic ozonation and mechanism study

In this work, a novel rGO/BiOCl-mediated photo-electrocatalytic ozonation process integrated from photocatalysis, ozonation and electrocatalysis has been demonstrated, resulting in the PFOA degradation up to 95.4% in 3h from synergistic effects of the efficiently generated h + and OH active species. • A combined photo-electrocatalytic ozonation is developed to remove PFOA up to 95.4%. • Synergistic effects of h + and OH account for the highly efficient PFOA degradation. • The novel rGO/BiOCl catalysts offer high E vb and effective charge-carrier separation. • The degradation intermediates are identified and quantified to unravel the mechanism. Perfluorooctanoic acid (PFOA) is a widely used perfluorinated compound that causes hazards to human health and environment, which is difficult to be removed by biological degradation. In this work, we demonstrate a highly efficient PFOA degradation process integrated from photocatalysis, ozonation and electrocatalysis, with rGO/BiOCl nanocomposites as catalysts. The PFOA removal ratio in 3 h reaches unprecedentedly 95.4%, superior to photocatalytic ozonation (80.5%) and photoelectro-peroxone process (56.1%). The mechanism of the enhanced catalytic activities has been detailedly investigated, which lies in synergistic effects of photo-generated hole (h + ) oxidation from photocatalysis and accelerated OH formation from cathodically generated H 2 O 2 . Through identifying degradation intermediates, it is revealed that decarboxylation of PFOA is rapidly initiated by strongly oxidative h + , forming unstable perfluoroheptyl radicals that are further transformed into shorter-chain perfluorocarboxylic acids by reacting with OH. This strategy will bring new insights into fields of catalysis and other related areas for environmental pollution abatement.

Degradation of Perfluorooctanesulfonate by Reactive Electrochemical Membrane Composed of Magnéli Phase Titanium Suboxide.

This study investigated the degradation of perfluorooctanesulfonate (PFOS) in a reactive electrochemical membrane (REM) system in which a porous Magnéli phase titanium suboxide ceramic membrane served simultaneously as the anode and the membrane. Near complete removal (98.30 ± 0.51%) of PFOS was achieved under a cross-flow filtration mode at the anodic potential of 3.15 V vs standard hydrogen electrode (SHE). PFOS removal efficiency during the REM operation is much greater than that of the batch operation mode under the same anodic potential. A systematic reaction rate analysis in combination with electrochemical characterizations quantitatively elucidated the enhancement of PFOS removal in REM operation in relation to the increased electroactive surface area and improved interphase mass transfer. PFOS appeared to undergo rapid mineralization to CO2 and F-, with only trace levels of short-chain perfluorocarboxylic acids (PFCAs, C4-C8) identified as intermediate products. Density functional theory (DFT) simulations and experiments involving free radical scavengers indicated that PFOS degradation was initiated by direct electron transfer (DET) on anode to yield PFOS free radicals (PFOS•), which further react with hydroxyl radicals that were generated by water oxidation and adsorbed on the anode surface (•OHads). The attack of •OHads is essential to PFOS degradation, because, otherwise, PFOS• may react with water and revert to PFOS.

Electrooxidation of short and long chain perfluorocarboxylic acids using boron doped diamond electrodes

This study investigates electrooxidation of short (C3-C6) and long (C7-C-18) chain perfluorocarboxylic acids (PFCAs) including perfluorooctane sulfonate (PFOA) using Si/BDD electrode. The effect of operational parameters (supporting electrolyte type, applied current density, and initial pH) were explored for PFOA removal. At the optimized conditions, 74% TOC removal and 37% defluorination ratio were gained for 10 mg L-1 of PFOA solution which evidences that the shorter chain PFCAs were formed. The PFOA degradation pathway followed one direct electron transfer from PFOA molecule to anode surface. Then two different degradation pathways were proposed. The first proposed degradation mechanism involved the reaction of perfluoroheptyl radical and hydroxyl radical, the release of HF and hydrolysis. The second mechanism involved the reaction between perfluoroheptyl radical and O2, formation of C7F15O and perfluorohexyl radical with releasing COF2. The removal of short- (C3-C6) and long-chain PFCAs (C7-C18) was also characterized. More than 95% of removal efficiency was gained for all long-chain PFCAs, excluding C7. The removal ratios of short-chain PFCAs (C3-C6) were 39%, 41%, 66% and 70% for C3, C4, C5 and C6, respectively. Contrary to long-chain PFCAs, chain-length dependence for short-chain PFCAs were observed. Defluorination ratio of short-chain PFCAs was only 45% signifying that defluorination partially occurred. Water matrix did not significantly affect the degradation of short-chain PFCAs in deionized water (DI), river water and secondary effluent of a wastewater treatment plant (WWTP). In contrast, defluorination ratio of long-chain PFCAs was noticeably affected by water matrix with the order of DI water > WWTP effluent > river water.

Aerobic biotransformation of 6:2 fluorotelomer sulfonic acid in soil

Per- and polyfluoroalkyl substances (PFASs) have been widely used in numerous industrial and household products due to its hydrophobic and lipophobic nature. As the main active ingredient, PFASs have been widely used in aqueous film forming foam (AFFF) used to fight liquid-fueled fires. As the electrochemical fluorination (ECF)-based PFASs were gradually phased out by major PFAS manufacturers worldwide, fluorotelomer-based PFASs, such as 6:2 fluorotelomer sulfonic acid (6:2 FTSA, [F(CF2)6CH2CH2SO3H]) and its precursors, have been widely detected in soil and groundwater effected by firefighting training activities. A few precursors (e.g., 6:2 fluorotelomer alcohol, 6:2 FTOH, [F(CF2)6CH2CH2OH]) have been well studied, but there are still leaving major gaps in understanding of 6:2 FTSA fate and aerobic biotransformation in soil. Soil collected from forest area was dosed with 6:2 FTSA to investigate its biotransformation rate and to identify major transformation products in a flow-through soil incubation system over 90 d. The overall mass balance at day 90 in sterile and live treatments averaged 97.4% and 76.8%, respectively, suggesting that there may be soil-bound residues and conjugates between fluorinated transformation products and dissolved soil components only in live test system not in the sterile soil. The 6:2 FTSA biotransformation was relatively low with a half-life more than 56 d, and 33% of initial 6:2 FTSA remained at day 90. According to the transformation products and the results in 6:2 FTSA biodegradation, the pathways of 6:2 FTSA aerobic biodegradation in the soil were proposed. The volatile 5:2 secondary alcohol (5:2 sFTOH, [F(CF2)5CH(OH)CH3]) and 5:2 fluorotelomer ketone (5:2 FT ketone, [F(CF2)5COCH3]) were the most abundant intermediate transformation products at the beginning, and reached highest at day 7 and 14, respectively. Perfluoropentanoic acid (PFPeA, [F(CF2)4COOH]) and perfluorohexanoic acid (PFHxA, [F(CF2)5COOH]) were produced as end products by 6:2 FTSA through desulfonation, oxidation and other reactions. In another minor pathway, 5:3 polyfluorinated acid (5:3 acid, [F(CF2)5CH2CH2COOH]) and perfluorobutanoic acid (PFBA, [F(CF2)3COOH]) were also formed. The concentrations of these end products, including PFBA, PFPeA, PFHxA, and 5:3 acid, increased in all experiment period. At day 90, the generations of PFPeA, PFHxA, 5:3 acid, and PFBA at a yield of 20.4 mol%, 6.5 mol%, 9.5 mol%, and 1.0 mol% were observed. Perfluoroheptanoic acid (PFHpA, [F(CF2)6COOH]) was not detected in the soil, suggesting that there was no α-oxidation in the process of 6:2 FTSA biotransformation in live soil. NaOH-acetonitrile extraction plus ENVI-Carb™ clean up could breakdown the binding between 5:3 acid and organic matter of the soil, and an enhancement factor up to 18 could be achieved for 5:3 acid by this cleanup method. The sorption of 6:2 FTSA to soil could low the biotransformation. The enzymatic desulfonation step may limit 6:2 FTSA biotransformation in aerobic soil. This study indicates that 6:2 FTSA may be persistent in aerobic soil, and a potential source of short chain perfluorocarboxylic acids (PFCAs) in soil. More studies need to be done to understanding the fate of AFFF-related polyfluoroalkyl precursors in soil environment in the future work.